Dial



United g States Patent DIAL Harald Valdemar Alexandersson, Lidingo, and Carl Oscar Sohlberg, Stockholm, Sweden, assignors to Telefonaktiebolaget L M Ericsson, Stockholm, Sweden, a corporation of Sweden Application August 30, 1956, Serial No. 607,206

Claims priority, application Sweden September 19, 1955 2 Claims. (Cl. 179-90) The present invention refers to a dial for automatic telephone systems having an impulse cam and an impulse contact actuated by said impulse cam when the dial is rotated.

The object of the invention is to provide a dial which is simple and reliable, runs quietly and sends impulses with accurately determined duration. A dial according to the invention is characterized by a blocking element following by frictional engagement part of the way at the I movement of the impulse cam, the blocking element having two shoulders and being arranged for movement between two end positions, one of the shoulders being arranged to keep the impulse contact independent of the impulse cam during movement of the dial in one direction and with the blocking element in one of its end positions, and the other shoulder being arranged to enable the impulse cam to be actuated by the impulse contact during the movement of the dial in an opposite direction and with the blocking element in its other end position.

The invention will be more closely described in connection with the enclosed drawing, where Fig. 1 shows, for the purpose of illustrating the invention, essential parts of a dial made in accordance with the invention, in an initial position. Fig. 2 shows the device according to Fig. 1, when the dial is partially rotated out of the initial position, Fig. 3 shows the device according to Fig. l, with the dial in an intermediate position moving back to the initial position from a first rotated position, whereby a blocking means begins to function in order to prevent too short a first impulse in the impulse series, and Fig. 4 finally shows the device according to Fig. 1, with the dial moving back to the initial position from a second position, whereby this second position is of such a kind, to prevent too short a first impulse in the impulse series.

In Fig. l, 1 is a cam disc directly connected by a shaft 2 to a finger wheel designed for the dialing of figures, but not shown on the drawing. The cam disc 1 is provided with a number of tooth grooves 3 and teeth 4, and a tooth 5 having larger radial extension than the teeth 4. A contact group with four springs 6, 7, 8 and 9 cooperates with the cam disc 1, the springs 6 and 7 of which together an impulse contact 6--7 for the real impulse generation provide and the remaining springs 8 and 9 make a shortcircuit contact 8--9 for bringing about a short-circuit function, which is necessary during the whole time the dial is brought out of its initial position. The spring 6 is provided with a shoulder 10 and a lifting stud 11, that lifts the spring 9, when the dial is in its initial position and the shoulder 10 rests against the tooth 5, thus breaking the short-circuit contact 8-9. A blocking means 12 is mounted on the cam disc 1, said blocking means having the shape of a sector-formed disc with two supporting shoulders 13 and 14 at the periphery of the disc. Because of the friction against the cam disc 1 the blocking means 12 is arranged to follow the same in its movement, but within a limited range, the extension of which is limited by two stops 15 and 16, between which the blocking means then can move.

When the dial is in its initial position, the various parts "ice assume the positions shown in Fig. 1. The impulse contact 6-7 is closed and the short-circuit contact 8-9 is broken. The blocking means 12 rests against the stop 16.

When a figure is dialed by means of the finger wheel and thereby the cam disc 1 is turned-in counter clockwise direction according to Fig. 2the blocking means 12 follows in the movement of the cam disc, until it hits the stop 15. During this movement of the cam disc 1 the impulse contact 6-7 remains closed, because the shoulder 10 rests against the supporting shoulder 14, which has a somewhat larger radial extension than the teeth 4 of the cam disc 1, but the short-circuit contact 89 is closed, because the shoulder 14 has a somewhat smaller radial extension than the tooth 5, whereby the lifting stud 11 can no longer lift the spring 9. During the whole movement of the cam disc in this direction the springs 6, 7, 8 and 9 keep the shown positions. As the impulse contact remains closed during the whole time of the winding up and furthermore lies still against the shoulder 14, a very quiet operation of the dial is obtained during rotation thereof. When the finger wheel is released and thereby the dial begins to return to its home position, an impulse series is generated, in the known way, by the co-operation between the cam disc 1 and the springs in the impulse contact, because the impulse contact 6-7 is closed when the shoulder 10 is passed by one of the teeth 4, but the impulse contact 6-7 is broken when the shoulder 10 is passed by a tooth groove 3, because the spring 6 moves then towards the cam disc 1 and the spring 7 remains mainly in rest position. At the shown embodiment the impulses in the impulse series are thought to correspond to the tooth grooves 3.

When dialing a number it may happen, however, that the finger wheel is not rotated sufiiciently, thereby causing the impulse series to begin with an impulse of shorter duration than the other impulses. This is prevented, however, by a dial according to the invention, as shown in Fig. 3, in which the parts are shown just when the cam disc 1 has begun its movementin clockwise direction towards the initial position. At the end of the rotation the shoulder 10 rests against the supporting shoulder 14 and is between two teeth 4. In response to movement in a clockwise direction the blocking means 12 follows the cam disc 1 in the beginning, the shoulder 10 slides then off the supporting shoulder 14, and both the springs 6 and 7 move together towards the cam disc 1, whereby an extension 71 of the spring 7, hits the edge of the supporting shoulder 13 and prevents the blocking means 12 from following the cam disc 1 for the present. No impulse has then been produced, in spite of the fact that the shoulder 10 has in any case passed a part of the tooth groove. At the continuing movement of the cam disc 1 the nearest following tooth 4 will lift both the springs 6 and 7, whereby the spring 7 is lifted sufliciently high to release the supporting shoulder 13 and thus the blocking means 12 can again follow the cam disc 1, until it is stopped by the stop 16, see also Fig. 4. After this the impulse generation continues in the usual way.

When the finger wheel is rotated by the dialing of a certain figure, as far as intended, i.e. the shoulder 10 stops over a tooth 3, the blocking means 12 follows immediately the cam disc 1 to the stop at the returning of the dial to the home position, and the impulse generation begins at the tooth groove 3, which follows nearest after the said tooth 4. This case is illustrated in Fig. 4.

We claim:

1. A dial for an automatic telephone system comprising, in combination, a shaft, a circular impulse cam mounted upon said shaft and having a plurality of spaced peripheral teeth and intermediate grooves, an impulse contact coacting with the periphery of said cam, said impulse cam being operative to actuate said impulse contact in reate-argues sponse to a rotation of said dial, blocking means mounted upon said shaft in releasable frictional engagement with said impulse cam for actuating said impulse contact, said impuise Contact permitting movement of said blocking means into the same direction .as said impulse cam in response to a movement of said impulse cam toward an initial position when a tooth of said cam is in engagement with said impulse contact, said impulse contact preventing movement of said blocking means towards said initial position when a groove of said cam is in association with said impulse contact and until continued rotation of said cam rotates one of said peripheral teeth into coacting relationship with said impulse contact.

2. A dial for an automatic telephone system as set forth in claim 1, wherein said blocking means has a pair of shoulders, a spring coacting with said impulse contact, a web supported between said shoulders, said cam teeth being spaced radially from the axis of said shaft a greater distance than said web, one of said shoulders being spaced References Cited in the file of this patent UNITED STATES PATENTS 2,691,070 Morris Oct. 5, 1954 2,691,071 MacCheyne Oct. 5, 1954 FOREIGN PATENTS 510,951 Great Britain Aug. 9, 1939 

